1. Field of the Invention
The invention relates to the use of a silicone fluid having a spreading coefficient of at least 2 mN/m to reduce foaming of hydrocarbon oils having a high saturates content. More particularly, the invention relates to the use of a silicone fluid having a spreading coefficient of at least 2 mN/m to reduce foaming of a hydrocarbon oil having a high saturates content, particularly a liquid wax isomerate, and to oil compositions containing a significant amount of same, including lubricating oils, such as industrial oils and internal combustion engine crankcase oil.
2. Background of the Invention
Lubricating oils (lube oils), including industrial oils and crankcase oils, used in environments in which the oil is subject to mechanical agitation in the presence of a gas entrap the gas in the form of small gas bubbles in the oil and as foam. Crankcase oils used in internal combustion engines represent a typical lube oil application in which the oil is subject to severe mechanical agitation which results in foaming and entrainment of air in the oil. Air entrainment and foaming of a lube oil can result in insufficient lubrication by preventing an effective amount of oil from reaching surfaces which are in need of lubrication. In addition to reducing the useful life of the oil due to enhanced oil oxidation, air entrainment in the oil also results in decreased engine life and increased fuel usage due to the reduced lubrication. Therefore, an antifoaming agent is added to lubricating oils used in such environments to reduce the foaming and air entrainment. Antifoaming agents must be effective over a fairly wide temperature range of from below freezing to temperatures above the boiling point of water, particularly when used with diesel and automotive crankcase oils. Some antifoaming agents eliminate foaming at lower temperatures, but not at higher temperatures and others are more effective at higher temperatures, but not lower temperatures. Increasing the amount of antifoamant may decrease the foaming tendency, but at the same time also increase the air release time of the oil. Silicone oils are known antifoamants and have been used to prevent foaming in a wide variety of lubricating oils, including industrial oils and diesel and automotive crankcase oils. However, while often (but not always) effective in reducing foaming, silicones degrade or increase the air release time of entrained air. Polyacrylates or acrylic polymers are also known antifoamants for oils and are disclosed in, for example, U.S. Pat. No. 3,166,508 and U.K. patent publication GB 2,234,978 A. Polyacrylates do not degrade the air release time of the oils to the same extent as the silicones do and have therefore replaced silicones in some applications. Unfortunately, polyacrylates are unpredictable in that they are effective with some oils, but not others. Fluorosilicones have been suggested for use as antifoaming agents in outgassing crude oils as disclosed, for example, in U.S. Pat. Nos. 4,329,528 and 4,626,378 and in British patent publication GB 2,244,279 A, but not for industrial or internal combustion engine crankcase oils.
More recently a new, premium class of hydrocarbon oil has been developed which is a wax isomerate, typically having a saturates content of greater than 99 wt %, and which is different in properties and composition than oils derived from crude oil distillates. One particular type of wax isomerate oil is derived from hydroisomerizing slack wax obtained by dewaxing a waxy petroleum oil fraction and is often referred to as a SWI, which stands for "slack wax isomerate". Lubricating oil compositions which contain one or more wax isomerate oils respond differently to antifoamants than do similar lube oils derived from crude oil distillates which do not contain a wax isomerate oil. Consequently, there is a need for being able to reduce low and high temperature foaming of a lubricating oil composition which contains a wax isomerate oil and preferably without degrading the air release time of the oil.